Laser Induced Breakdown Spectroscopy (LIBS) is a powerful tool for qualitative and quantitative elemental, molecular and even isotopic analysis of materials. LIBS uses pulsed, solid state, lasers such as those made from Neodymium doped Yttrium Aluminum Garnet to generate short, powerful pulses that initiate dielectric breakdown on solids, in liquids and gases. This dielectric breakdown produces a bright flash of light at wavelengths that are characteristic of the elements present in the target. When the light is analyzed by a spectrometer, the identities of the elements present can be estimated and can be quantified when a gated spectrometer is used.
In LIES, the analysis operates by focusing the laser onto a small area at the surface of the specimen or into the specimen (gas/liquids), when the laser is discharged it ablates a very small amount of material, in the range of nanograms to picograms, which generates a plasma plume with temperatures typically in excess of 10,000 K. The local electric field density within the focal volume ionizes the molecules and element within it creating a large thermos-luminescent emission initially. The relations or cooling of the hot gas allows for electron recombination. It is this process that releases the characteristic energy. During data collection, preferably after local thermodynamic equilibrium is established, plasma temperatures range from 5,000-20,000 K. At the high temperatures during the early plasma, the ablated material dissociates (breaks down) into excited ionic and atomic species. During this time, the plasma emits a continuum of radiation which does not contain any useful information about the species present, but within a very small timeframe the plasma expands at supersonic velocities and cools. At this point the characteristic atomic emission lines of the elements can be observed and the characteristic radiation evaluated.
Prior art LIBS probe systems require an aligned intracavity Q-switch to generate the high peak power laserpulses. The Q-switching may be performed by an electro-optical or acoustic-optical element or a solid state saturable absorber known as a passive Q-switch. However the use of a Q-switch requires that the housing of the LIBS probe come equipped with at least four mirrors. The mirrors allow the LIBS light to bypass the laser rod and couple back into the fiber optic cable pumping the laser. Two of the four mirrors need to be dichroic mirrors produced through an extensive chemical vapor deposition process.
Therefore, a need persists in the industry for a LIBS system that avoids the need for four mirrors and attendant alignment, thereby reducing the complexity and the cost of the laser head.